Merge pull request #8 from nabetama/channels

Channels
ChatDelete
ChatPostMessage
ChatUpdate
Merge pull request #9 from nabetama/chat

Chat
Emoji
Merge pull request #10 from nabetama/emoji

Emoji
Files
Merge pull request #11 from nabetama/files

Files
Improve error handling.
Merge remote-tracking branch 'origin/master'
FilesUpload
Merge pull request #12 from nabetama/files

FilesUpload
Groups
GroupsArchive, GroupsList
Merge pull request #13 from nabetama/groups

Groups
GroupsClose
GroupsCreate
GroupsCreateChild
GroupsHistory
Merge pull request #14 from nabetama/groups

Groups